High speed texturing of synthetic continuous filament yarn

ABSTRACT

A filamentary yarn is false twist textured by being heat set in a twisted configuration. The twist is imparted to the yarn by contact with the inner surface of a rotating friction insert having a profiled friction surface, the insert being mounted in a rotatable cup. The threadline contacts the friction surface at an angle to the surface and passes from the friction surface through a guide and out of the interior of the friction insert.

United States atent 1191 Holland et al..

1 51 Apr. 3, 1973 [54] HiGH SPEED TEXTURING 0F SYNTHETIC CONTINUOUS FILAMENT YARN [75] Inventors: Charles E. Holland, Lincolnton; Robert E. Hinson, Jr.; Richard V. Putnam, both of Charlotte, all of [73] Assignee: Celanese Corporation, New York,

[22] Filed: May 28, 1970 [21] Appl. No.: 41,436

52 US. Cl. ..57 77.4, 57/34 HS, 57/157 TS 51 Int. Cl. ..D02g 1/04 58 Field of Search ..57/34 R, 34 ns, 38.4, 51, 51.6,

3,527,043 9/1970 Sabaton ..57/77.4 2,590,374 3/1952 Brown. 3,462,938 8/1969 Mehta ..57/34 X Primary Examiner-Werner l-l. Schroeder Attorney-Thomas J. Morgan, Stephen D. Murphy 5 and Andrew F. Sayko, Jr.

57 ABSTRACT A filamentary yarn is false twist textured by being heat set in a twisted configuration. The twist is imparted to the yarn by contact with the inner surface of a rotating friction insert having a profiled friction surface, the insert being mounted in a rotatable cup. The threadline contacts the friction surface at an angle to the surface and passes from the friction surface through a guide and out of the interior of the friction insert.

11 Claims, 18 Drawing Figures PATENTEI] APR 3 I975 SHEET 10F5 INVENTORS RICHARD V. PUTNAM ROBERT E. HINSON, JR. CHARLES E. HOLLAND 7 Ii/5U PATENTEDAPR3 ms 3.724.196

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SHEEI 5 OF 5 PATENTED APR 3 I975 INVWORS RlCHARD V. PUTNAM ROBERT E. HINSON, JR.

CHARLES E. HOLLAND M7 A, OR/Vfy HIGH SPEED TEXTURING OF SYNTHETIC CONTINUOUS FILAMENT YARN The present invention relates to improvements in or relating to the twisting and crimping of textile filaments. It particularly relates to an improved apparatus and process of false twist texturing utilizing a substantially circular cup-type friction insert.

False twist spindles have been in use in the textile industry for a number of years and recently they have found particular use in crimping thermoplastic textile filaments by a continuous twisting, setting and back twisting sequence. Heat is applied to the filaments while they are in the highly twisted condition to set the twist, so that when the equal and opposite twist of the untwisting occurs after the filaments leave the false twist spindle, crimping occurs. The principle upon which false twist spindles have operated is to cause the running filaments to acquire the rotational motion of the spindle by means providing for contact with parts of the inside of the hollow spindle whereby each revolution of the tube applies one revolution to the filaments.

A bore in the spindle itself may be made eccentric over some part of its width (i.e., not along the axis of rotation) so that the filaments are caused to acquire rotation of the motion of the tube by taking a short path away from the axis of rotation. In other spindles, the filament enters through a radial hole at one end, that is, through a hole displaced radially from the axis of rotation of the spindle. The amount of twist which can be inserted in the running textile filament by means of such process is obviously limited by the rotational speed of the false twist spindle. High rotational speeds of such false twist spindles create difficulties relating to their construction and maintenance.

It is alsoknown to impart false twist to a textile filament by causing the filament to bear against and be rotated by the inner peripheral surface of at least one end portion of a rotating false twist bushing an one side of the axis thereof by leading the filaments towards and away from the bushing to a guide. The internal surface of the bushing, at least at its yam-contacting end-portion, is composed of a nonabrasive material having a high coefficient of friction with the filament. Thus, if the filament is held steady in the same relative position on the periphery of the tube, the ratio of the rotational speed and the filament to that of the tube will depend on the ratio of the inner diameter of the tube to the diameter of the filament.

In such an arrangement, the threadline passes through the false twist bushing in a continuous path, requiring that the threadline be broken to accomplish threading. Also, high rotational speeds are difficult to attain in such arrangements, because bearings must necessarily be larger than the inside diameter of the twist tube. It is quite often necessary to resort to exotic and expensive components, such as air bearings, to attain high rotational speeds. In all these systems, the attainment of high twist levels requires low threadline speeds at drawdown and a critical limitation for spin draw operations.

Alternatively, the filaments may run in contact with the external surface of a rotating member having a plurality of friction disks rotating about a common shaft, the filaments running obliquely to the direction of rotation of said surface.

It is important to maintain the filament direction substantially constant, which in this system requires disposing a guide just prior 'to the friction surface. The guide is necessary because there is no force to stabilize the threadline path when the yarn is running on the outer surface of the friction disks. The threadline will tend to slide down the friction disk to take the path of lower resistance. Thus, the guide is necessary to maintain a substantially constant threadline path to provide a yarn having substantially uniform false twist.

The use of a guide has the disadvantage that it raises the torsional resistance to the threadline and acts as a twist trap necessitating the use of higher tensions to achieve the required turns per inch false twist.

It is therefore an object of this invention to provide a high speed friction false twist texturing process wherein the speed is not limited by the mechanical stresses placed upon a yarn in a false twist spindle texturing process.

It is a further object of this invention to provide a friction false twist texturing process capable of texturing relatively low strength yarns, e.g., cellulose ester yarns, without harm, by eliminating the need for imparting a force (drag) on the yarn to pull the yarn across the friction surface in the direction of yarn travel.

It is another object of this invention to provide a friction false twist texturing process wherein the tension upstream of the friction surface may vary with relation to the tension downstream, e.g., the friction surface itself can function as the yam-forwarding means.

It is yet another object of this invention to provide a false twist texturing apparatus and process wherein the twist is imparted by static rolling friction generated by a substantially nonslipping contact between the yarn and the friction surface.

It is a further object of this invention to provide a self-stabilizing apparatus and process which precludes the need for guides (which act as twist traps) near the false twist means.

It is another object of this invention to provide a friction false twist texturing process and apparatus wherein the speed of rotation of the friction insert is relatively small as compared with the rate of rotation of the yarn bundle.

It is a further object of this invention to provide a completely in-line texturing operation utilizing a variable length tubular yarn heater in combination with the friction false twist texturing apparatus of this invention.

Other objects will become apparent from the following detailed description and claims.

In the present invention, a filamentary yarn is false twist textured by contacting the yarn with the inner surface of I a rotating friction insert. The threadline preferably contacts the friction surface of the friction insert at an angle to the surface (i.e., of from about to to the axis of rotation of the friction insert), the threadline is twisted in contact therewith and then passes from the surface through a guide and out of the interior of the friction insert, not in contact with the friction surface. The false twist is substantially imparted to the yarn by static rolling friction generated by a substantially nonslipping contact between the yarn and the rotating friction surface. This static rolling friction imparts to the yarn both a torsional force and a longitudinal force in the threadline direction; When the angle at which the yarn passes across the friction surface is substantially equal to the twist angle of the yarn, the threadline passes across the friction surface with a rolling motion rather than a sliding motion, which substantially eliminates yarn abrasion. The friction insert is mounted in a cup-type holder mounted for rotation.

The cup-type holder must be a radially symmetrical hollow rotatable member'having a substantially circular opening at least at one end. The axis of rotation of the opening is coincidental with the axis of symmetry of the cup-type holder and the axis of symmetry of the holder is coincidental with the axis of rotation of the holder. A friction insert is mounted within the opening in the cup-type insert so that the axis of symmetry of the insert and the holder coincide. The insert and holder may also be integral so that the insert is not removable. The friction surface of the insert is composed of a nonabrasive material having a high coefficient of friction with the textile filaments to be twisted. Suitable materials include: natural rubber, silicone rubber, polyurethanes, ionomer and other rubber-like materials. Ceramic, or other wear-resistant materials, may be added in dispersion or on the surface of the friction insert. Low modulus filamentary materials, such as cellulose triacetate, are particularly susceptible to abrasive damage in such operations and must be textured under generally low tension. A friction surface characterized by a durometer hardness of less than about 60, preferably from about to 40 (shore rating, scale A, ASTM-D-2240) and a high effective coefficient of friction with the filaments have been found especially'suitable for yarns having a Young's modulus of less than about 45 and this constitutes a feature of this invention.

A thorough understanding of the invention may be facilitated by reference to the accompanying drawings forming a part of this specification in which:

FIG. 1 is a sectional partial schematic representation of the false twist texturing process of this invention;

FIG. 2 is a sectional view of a variable length yarn heater useful in the false twist texturing process of this invention;

FIG. 3 is a perspective view of the assembly of the cup-type holder and the friction false twist insert showing the threadline passing around the internal guide both in and out of contact with the friction surface;

FIG. 4 is a sectional elevation view of the assembly of the holder and the friction false twist insert of FIG. 3 along line 4-4;

FIG. 5A is a sectional view of the friction surface of a friction insert, wholly contained in the second quadrant of a reference circle;

FIG. 5B is a partial sectional elevation of the friction surface shown in FIG. 5A and the path the yarn takes across this surface;

FIG. 5C is a graph showing the surface speed across the friction surface shown in FIG. 5B;

FIG. 6A is a sectional view of the friction surface of a friction insert, wholly contained in the first quadrant of surface shown in FIG. 6B;

FIG. 7A is a partial sectional elevation of a friction false twist bushing utilized in the prior art;

FIG. 7B shows the surface speed of a threadline moving across the surface of the friction false twist surface shown in FIG. 7A;

FIG. 8A is a partial sectional elevation of another friction false twist bushing utilized in the prior art;

FIG. 8B shows the surface speed of a threadline moving across the surface of the friction false twist surface shown in FIG. 8A;

FIG. 9 is an illustration of the forces and angles involved when the yarn passes over the friction surface;

FIG. 10 is a schematic illustration of the friction insert RPM, threadline RPM and threadline linear velocity;

FIG. 11 is a graph of the helical path the yarn takes across the friction surface when the helix is unwrapped from the surface of the threadline;

FIG. 12 is an illustration of the variables involved when mathematically defining the friction surface utilized in the apparatus and process of this invention.

FIG. 1 discloses a specific embodiment of the subject invention. The yarn to be false twist textured 2 was fed from package 1 through pigtail guide 3 by rollers 5 and 6, around guides 7 and 8 through tubular yarn heater 9 to profiled friction surface 11 of rotating cup-type friction insert 10, held by cup-type holder 18. The yarn then passes from the friction surface through guide 12 and out of the interior of the friction insert, not in contact with the friction surface to rolls l4 and 15 or suitable take-up rolls. The cup-type holder carrying the friction insert is rotated by a suitable means on shaft 13. The yarn is taken up on package 16 driven by drive roll means 17. Guide l2 is movable as shown inFIG. 3, so that theyam may be threaded up when the guide is outside of the friction insert, then positioned within the insert to contact the yarn with the friction surface.

FIG. 2 shows a variable length tubular yarn heater especially useful in conjunction with the high speed false twist texturing process and apparatus of this invention. The yarn heater 25 may be infinitely varied as to the effective heater length, limited only by the absolute height of the heater. The yarn is passed around roll 30 and is threaded through guides such as pigtail guides 22 and 23. The guides are mounted in block 21 which is attached to line 26, which may be rope, wire, etc. The block 21 containing pigtail guide 22 and 23 is raised to the desired column height after the yarn to be textured is threaded through the guide by means of member 29 which may be a pulley or other suitable apparatus. Winding the pulley 29 moves the line 26 either up or down around rollers 27 and 28 to achieve the desired column height. The use of such a variable length yarn heater which, with its easy threadup in conjunction with the friction insert assembly of this invention, allows a completely in-line operation wherein one operator at a single location can easily threadup the false twist texturing apparatus in a very short period of time. Corrections in heating conditions may be accom-- plished when running, even automatically as by interconnecting two appropriate heat sensors downstream.'

FIG. 3 shows the friction false twist insert 10 FIG. 4 is a view of the friction false twist insert assembly of FIG. 3 along line 44. The yarn 2 contacts friction surface 11 of friction insert 10, thereby false twisting the yarn. The yarn passes from friction surface 1 l to internal guide 12 and passes out of the interior of the friction insert not in contact with friction surface 11. The cup-type friction insert is mounted in cup 18 on drive shaft 13 in bearing support 41 driven by pulley 42.

FIG. 5B shows how friction surface 51 wholly contained in the second quadrant of a reference circle, as shown in FIG. 5A, stabilizes the threadline 2 by causing the threadline path to follow a straight skew line 52 across the inner surface 51 of the friction insert. Therefore, the threadline 2 and the skew line 52 are maintained at a substantially constant angle 6 with respect to the plane 53 perpendicular to the axis of rotation of the insert.

FIG. 6B shows how friction surface 61 wholly contained in the first quadrant of a reference circle, as shown in FIG. 6A, stabilizes the threadline 2 by causing the threadline path to follow a straight skew line 62 across the inner surface 61 of the friction insert. Therefore, the threadline 2 and the skew line 62 are main tained at a substantially constant angle 6 with respect to the plane 63 perpendicular to the axis of rotation of the insert.

FIG. 7A shows how surface profile 71 causes threadline 2 to substantially deviate from straight skew line 72 and varies the angle 0, with respect to the plane 73 perpendicular to the axis of rotation of the insert.

FIG. 8A shows how profile 81 causes threadline 2 to substantially deviate from skew line 82 and varies the angle 0 with respect to the plane 83 perpendicular to the axis of rotation of the insert.

FIG. 9 is an illustration of the forces and angles involved when the yarn passes over the friction surface.

Nomenclature r Nominal thread radius R Radius from the first edge of the friction insert contacted by the threadline d Nominal threadline diameter D Inside diameter of friction insert containing friction surface V Threadline linear velocity or feed rate (longitudinal force) N Friction insert RPM N Threadline RPM (generated by torsional force) The angle 0 is the angle between the plane 93 perpendicular to the axis of rotation of friction insert and the threadline path across friction surface 11. As is seen from the diagram, the threadline longitudinal velocity component (straight skew line) is substantially coincidental with the threadline path across the friction surface, both of which are at a substantially constant angle 6 to line 93, both entering and exiting from the friction surface.

FIG. 10 shows the threadline velocity V (longitudinal force), the friction insert RPM N and the threadline RPM N (torsional force) and the direction of the longitudinal and torsional forces generated by each component.

FIG. 11 is a graph of the helical path the yarn takes across the friction surface when the helix is unwrapped from the surface of the threadline. In FIG. 11:

11; is the angular displacement of the threadline in radians. L is the length of the helix per 2 1r radians of revolution. h is the linear height of the helix per 2 1r radians of revolution.

Y is the vertical axis of the graph.

In order to carry out the false twisting continuously and uniformly, the filaments must be simultaneously subjected to a torsional force and a longitudinal force (i.e., skewed). It is necessary that the motion of running the filaments in contact with the frictional surface of the rotating member be smooth and that the threadline path be maintained substantially constant. The threadline passes over the friction surface at an angle 4);, from its axis and in contact with the rubber inner surface. The optimum condition is reached when the angle isequal to the helix angle of the filaments in the twisted threadline. This, in turn, is a function of threadline linear speed and rotational speed imparted by the friction insert. Therefore, for any given linear speed and helix angle, determined by the twist in turns per inch (I.P.I.) desired, the R.P.M. of the friction insert is set to impart the required T.P.I. in the threadline. Varying the R.P.M. of the insert varies the T. P.l. of the threadline, but because the threadline is skewed across the friction surface, the skew angle also varies but the longitudinal force on the threadline remains substantially the same as the threadline speed just prior to contacting the friction surface. In addition, the internal guide is preferably rotatably mounted so that upon rotation, the path across the friction surface can be varied to either increase or decrease the skew angle and, as a result, vary the T.P.I. of the threadline as well as the longitudinal and torsional force components on the threadline. Thus the threadline passes through the bushing with a rolling motion, rather than a sliding one, eliminating abrasion. Heating then cooling the thread ahead of the friction insert allows the texturing of yarn at speeds of at least three times those previously possible by spindle-type false twisters.

The following relations can be seen from FIG. 9, l0 and 1 l:

L= 21rr/Cos (1);, 21'rr/Sin (1);,

h L Cos 0 and by a similar triangle analysis L can be replaced by dL/dz and h can be replaced by dy/dt if 2'n'r is replaced by dll /dt It can also be seen that dy/dt.= V 5 the linear velocity of the thread.

Making'these substitutions in eq. (3)

V= W flTan 0 =2irNrlTan65 21.1 cotea/sin 03 7 I From the method of gear analysis it can be seen that N,/N =L/2'rrR Substituting l into (7), we get N /N 21rr/21rR Sin 6 r/R Sin 6;, a

and

N =N R Sin 6;, /r

making this substitution into (6) (N lii 7Sin 9 COS V: 63

Cos 0 V/2'n-R,l l (9 and if we let P be the desired twist per inch, then P= N /V and Cos. 6 NJZ 'rrR PN, 11

Substituting (8) into l 1) Cos. 6 R Sin 6;, 21rR Pr= Sin 6 /21rPr and Tan 0 21rPr Thus 6 =Tan -(1rPd) 12 for no relative motion between the Twisting Friction Insert and the point of contact with the thread.

For setting up and evaluating the system, the following sequence of equations is useful;

0 Tan (n-Pd) N V/21rR Cos 6 Where V, R, P, and d are the desired parameters of the system.

the point of least resistance or force. Any substantial deviation from this path will result in greater tension on the yarn and the yarn will then tend to restore itself to the path of least resistance.

The threadline approach angle to the interior friction surface of the friction insert with relation to the axis of rotation of the friction insert may vary from about 75 to 105. Thus, when the threadline path comes virtually straight down or slightly tilted toward the friction insert, the geometry is such that this permits maximum wrap, i.e., maximum contact with the friction surface. When the threadline achieves this maximum contact, the rolling static friction serves to aid in maintaining a substantially constant threadline path. The dynamic effects of the torsional force imparted to the yarn by the friction surface tend to cause the threadline path to move. However, the static rolling friction and longitudinal force component generated by yarntension are sufiicient to overcome the torsional force and prevent any substantial shifting of the threadline path.

The total width of the friction surface of the friction insert must be greater than the diameter of the interior opening of the insert. This enables the threadline to be tilted prior to contact toward or away from the friction surface and still maintain contact over substantially the whole width of the friction surface for maximum sta bility'in the threadline path and close adherance to the skew line. Therefore, the ratio of the diameter of the interior opening of the substantially circular friction insert to the width of the friction surface contacted should be greater than one and may be as high as 40 or more. Preferably this ratio is from 2 to 40, for optimum false twist texturing.

The friction surface is the interior the friction insert and the threadline passes over the inner surface of the substantially circular insert. Should the threadline momentarily stray, the curvature of the surface produces a force restoring the threadline to the path of least force, which substantially stabilizes the contact area. The cross-section of the friction surface is defined by an arc wholly contained in either the first or second quadrant of a reference circle, such as shown in FIGS. 5A and 6A, preferably the second quadrant. The single quadrant surface stabilizes the threadline path on the friction surface by causing the yarn to adhere to the skew line as it moves across the surface, as shown in FIGS. 53 and 6B. This may be attributed to the slope of the friction surface which is either continuously positive or negative, but not both. For such a friction surface, the velocity or surface speed vector is relatively flat, i.e., fairly constant (as shown in FIGS. SC and 6C) across the friction surface as compared with velocity profiles (such as shown in FIGS. 7A and 8A) of friction false twist texturing surfaces utilized previously, as shown in FIGS. 73 and 8B. This velocity profile, with its characteristic lack of drastic change in surface speed across the threadline path, leads to a more uniformly bulked yarn and a more stable texturing process.

As seen from FIG. 12, there are 5 geometrical parameters of interest which describe the friction surface profile. These are:

l. r perpendicular distance from axis of rotation A.

2. r perpendicular distance of back edge of insert from axis of rotation A.

3. R= radius of curvature of insert inside surface.

of front edge of insert 4. angle between plane containing front edge of the insert and a line drawn from the axis of rotation A, perpendicular thereto, to center of curvature B of the insert inside surface.

5. 6 angle between plane containing the back edge of the insert and a line drawn from the axis of rotation A, to the center of curvature of insert inside surface (B).

To fully define a quadrant insert inner surface, any four of these parameters can be specified. If this is done, the fifth parameter becomes a dependent quantity which is not needed to specify the surface.

The five parameters are related to the following:

5. X= RCos 0 R Cos 6 =R(Cos 0 Cos 6 6. r r R(Cos 6 Cos 0 7. r,/r r /[r R(Cos 6 Cos 0 and for the quadrant insert to perform satisfactorily, i.e., provide a relatively flat velocity profile and a substantially stable threadline path wherein a is less than or equal to 1.10, preferably 1.05

For inserts in the second quadrant, 0 and 6 must be measured in the opposite sense.

Friction surfaces having a quadrant profile, as defined by the formula:

r R (Cos 0 C0s 0 sl'lo provide a continuously curved surface allowing maximum continuous stable contact between the threadline and the friction surface while at the same time exhibiting a relatively flat velocity profile across the surface. The surface must present a substantially circular profile as defined in the above formula and cannot be flat. The threadline progresses diagonally across the profiled friction surface as described in the above formula, wherein a is less than, or equal to, 1.10. The threadline path substantially conforms to the surface and is preferably in contact therewith across substantially the whole width of the friction surface. A flat surface produces a ballooning phenomenon at the high speeds characteristic of the process of this invention. This ballooning phenomenon causes the yarn to flail back and forth across the friction surface. When this instability in the threadline path becomes excessive, filament breakage often occurs.

Even with the profiled surface, the yarn-to-friction surface pressure is generally highest at the entry and exit edges. It is thought that because the greatest normal force is at the edges, the torque transmission is greater so that a substantial percentage of the total twist is imparted at the entry to the friction surface. A friction surface profile with sharp edges would be more efficient for twisting the yarn. However, radiused or rounded edges which present a larger initial contact surface are preferred for greater resistance to wear. A radiused edge tends to spread out the initial torque transmission over a relatively smooth surface. The radiused edges blend into the rest of the friction surface such that a continuous surface is presented to the yarn being false twisted. The friction surfaces preferably have a minimum edge radius having a rate of curvature (greater than the rate of curvature of the interior friction surface) of about one sixty-fourth of an inch length, up to about one-fourth inch, preferably from about one thirty-second inch to one-sixteenth inch, wherein the sides and the interior surface of the insert are tangential to the arc defining the radiused edge.

The yarn, preferably, initially contacts the radiused edge and the interior friction surface on one axial side of the rotating friction insert, passes over the friction surface to the internal guide, passes through or around the guide and is passed out of the interior of the insert on the same axial side of the rotating friction insert.

Any filamentary material of regular or irregular cross section may be false twist textured in accordance with this invention. Although suitable for use with e.g. polyesters or polyamides, it is especially adaptable to low modulus yarns such as cellulose acetate or acrylics. The continuous high speed process may be employed to produce conventional stretch yarn or may be modified as by the interposition of additional heating, cooling or twisting steps often in conjunction with the provision of additional tension control in such steps to provide a wide variety of textured products. One such useful modification calls for the use of a stabilizing heater between rolls 15 and 16 and the take-up, which may be employed in a separate relax zone provided by an additional set of speed and tension controlling rolls prior to the package. Particularly effective results have been secured employing e.g., polyester yarn of 150 denier/40 filaments with an overfeed of from about -2 to +4 percent across the false twist bushing and an overfeed across the heater of from about +1 1 to +17 percent and twist levels of from about 60 to turns per inch and running speeds of from about to yards per minute with a heater residence time of from about 0.3 to 0.6 seconds. The yarn is heat set while it is in a twisted state, to set the crimp, and then untwisted.

The invention is further illustrated by the following examples:

EXAMPLE I Referring to FIG. 1, a continuous multi-filament plied yarn 2, consisting of 79 denier percent /22 cellulose triacetate and about 1 denier percent 40/13 nylon 6,6, containing 35 filaments, having a total denier of was fed from package 1 through pigtail guide 3 by rollers 5 and 6 then around guides 7 and 8 at a speed of 600 meters per minute (an underfeed of 7.1 percent). The yarn 2 was fed through tubular yarn heater 9 which was maintained by an electrical heater at a temperature of about 2l0centigrade and which had a selected treating height of about 9 /2 feet for a residence time of about 0.3 seconds. The yarn was then passed to profiled friction surface 11 of rotating friction insert 10 made of a silicone rubber. The friction insert was rotating at a speed of about 2,600 r.p.m. The yarn then passed from the friction surface of the insert through internal yarn guide 12 and out of the interior of the friction insert, not in contact with the friction surface, to rolls l4 and 15. The tension upstream of the point of contact with the friction insert was maintained at 49 grams which was equal to the downstream tension. The yarn was then taken up at 600 meters per minute (a second overfeed of +4.9 percent) on package 16 driven by roll 17. The resultant cellulose v triacetate/nylon combination yarn had a false twist level of about 36 turns per inch.

The yarn approached the friction surface at an angle of about 90with respect to the axis of rotation of the friction insert. The surface profile was defined by the formula:

a= r /[r R(Cos 6 Cos 6 wherein 9 16, 2, R 2.5 inches, r 2 inches so that a 1.049.

EXAMPLE 11 A continuous multi-filament yarn of nylon 6,6 having a total denier of 40 and containing 13 filaments was fed from package 1 through pigtail guide 3 by rollers 4 and 5 then around guides'6 and 7 at a speed of 500 meters per minute (an underfeed of 4 percent). The yarn 2 was fed through tubular yarn heater 8 which was maintained at a temperature of about 220centigrade and which had a selected height of about 7% feet for a residence time of about 0.2 seconds. The yarn was thenpassed to friction surface 11 of rotating friction insert 10. The yarn approached the friction surface at an angle of about 85with respect to the axis of rotation of the friction insert. The friction surface was identical to the surface of Example 1. The friction insert was rotating at a speed of about 2,500 r.p.m. The yarn then passed from the friction surface of the insert through internal guide 12 and out of the interior of the friction insert, not in contact with the friction surface, to feed rolls l4 and 15 The tension upstream of the point of initial contact with the friction insert was maintained at 16 grams, which was equal to the downstream tension. The yarn was then taken up at 505 meters per minute (a second overfeed of +3.2 percent) on package 16 driven by roll 17. The resultant nylon yarn had a false twist level of about 92 turns per inch.

EXAMPLE III A continuous multi-filament yarn 2 consisting of cellulose triacetate having a total denier of 150, containing filaments and having a twist of 2 turns of Z twist per inch, was fed from package 1 through pigtail guide 3 by rollers 4 and 5, then around guides 6 and 7 at a speed of about 470 meters per minute (an underfeed of l 2 percent). The yarn 2 was fed through tubular yarn heater 8 which was maintained at a temperature of about l80 centigrade and which had a selected height of about 6 feet for a residence time of about 0.25 seconds. The yarn was then passed to friction surface 11 of rotating friction insert 10. The yarn approached the friction surface at an angle of about 90 with respect to the axis of rotation of the friction insert. The

friction surface was identical to the surface of Example 1. The friction insert was rotating at a speed of about 2,000 r.p.m. The yarn then passed from the friction surface of the insert through internal yarn guide 12 and out of the interior of the friction insert, not in contact with the friction surface, to feed rolls l4 and 15. The

tension upstream of the point of initial contact with the friction insert was maintained at about 56 grams, which was equal to the downstream tension. The yarn was taken up at about 504 meters per minute (a second overfeed of +6 .percent) on package 16 driven by roll 17. The resultant cellulose triacetate yarn had a false twist level of 40 turns per inch.

EXAMPLE IV A continuous multi-filament yarn of nylon 6,6 having a total denier of and containing 34 filaments was fed from package 1 through pigtail guide 3 by rollers 4 and 5 then around guides 6 and 7 at a speed of 300 meters per minute (an underfeed of -4.2 percent). The yarn 2 was fed through tubular yarn heater 8 which was maintained at a temperature of about 220 centigrade and which had a selected height of about 9 feet for a residence time of about 0.4 seconds. The yarn was then passed to friction surface 11 of rotating friction insert 10. The yarn approached the friction surface at an angle of about with respect to the axis of rotation of the friction insert. The friction surface was identical to the surface of Example 1. The friction insert was rotating at a speed of about 3,700 r.p.m. The yarn'then passed from the friction surface through internal guide 12 and out of the interior of the friction insert, not in contact with the friction surface of the insert, to feed rolls l4 and 15. The tension upstream of the point of initial contact with the friction insert was maintained at 37 grams, whereas the downstream tension was 30 grams. The yarn was then taken up at 290 meters per minute (a second overfeed of +8 percent) on package 16 driven by roll 17. The resultant nylon yarn had a false twist level of 82 turns per inch. 2

EXAMPLE V The continuous multi-filament plied yarn 2 of Exam pic I was fed from package 1 through pigtail guide 3 by rollers 4 and 5, then around guides 6 and 7 at a speed of about 500 meters per minute (an underfeed of 6 percent). The yarn 2 was fed through tubular yarn heater 8 which was maintained at a temperature of about 210 centigrade and which had a selected height of about 9% feet for a residence time of about 0.35 seconds. The yarn was then passed to friction surface 11 of rotating cup-type friction insert 10. The yarn approached the friction surface at an angle of about 90 with respect to the axis of rotation of the friction insert. The friction surface was. identical to the surface of Example I. The friction insert was rotating at a speed of about 2,200 r.p.m. The yarn then passed from the friction surface of the insert through internal yarn guide 12 and out of the interior of the friction insert, not in contact with the friction surface, to feed rolls l4 and 15. The tension upstream of the point of initial contact with the friction insert was maintained at about 37 grams, whereas the downstream tension was about 30 grams. The yarn was taken up at about 511 meters per minute (a second.

overfeed of +4 percent) on package 16 driven by roll 17. The resultant cellulose triacetate/nylon yarn had a false twist level of about 37 turns per inch.

What is claimed is:

1. A process for false twisting yarn by heat setting while it is in a twisted state which comprises advancing a yarn under tension from a source thereof through a temperature zone, contacting said yarn with the interior profiled friction surface of a hollow rotating member, imparting to said yarn both a torsional force and a longitudinal force in the direction of yarn traveled by progressing said yarn diagonally across said wherein a is less than, or equal to, 1.10 and wherein:

r is perpendicular distance of front edge of friction surface from axis of rotation;

R is radius of curvature of friction surface;

6 is angle between plane containing front edge of the friction surface and a line drawn from the axis of rotation, perpendicular thereto, to center of curvature of the friction surface;

is angle between plane containing the back edge of the friction surface and a line drawn from the axis of rotation, to the center of curvature of friction surface;

and simultaneously false twisting said yarn by a substantially static rolling friction generated by a substantially nonslipping contact between said yarns and said rotating friction surface, passing said yarn from said interior profiled friction surface and guiding said yarn under tension out of said interior friction surface on the said side it entered into contact with said friction surface.

2. The process of claim 1 wherein the threadline initially contacts said friction surface on one side of said rotating member and is guided out of the interior of said rotating member on the same side of said rotating member, not in contact with said friction surface.

3. The process of claim 1 wherein the tension upstream of the point of initial contact with the interior profiled friction surface of said rotating member is substantially equal to the downstream tension.

4. The process of claim 1 wherein the yarn approaches the profiled friction surface of the rotating member at an angle of from about 75 to 105 with respect to the axis of rotation of said rotating member.

5. The process of claim 1 wherein a is less than, or equal to, 1.05.

6. The process of claim 1 wherein the yarn contacts the friction surface across substantially the whole width of said friction surface.

7. An apparatus for imparting false twist to textile filaments comprising a radially symmetrical, rotatable member having a substantially circular opening at at least one end thereof, the axis of rotation and axis of symmetry of said rotatable member being coincidental with the axis of symmetry of said circular opening, a friction surface within said opening of said member with said surface having a surface profile defined by the following formula:

r /[r R(Cos 6 Cos 0 =a wherein a is less than, or equal to, l. 10 and wherein:

r, is perpendicular distance of front edge of friction surface from axis of rotation;

R is radius of curvature of friction surface;

0 is angle between plane containing front edge of the friction surface and a line drawn from the axis of rotation, perpendicular thereto, to center of curvature of the friction surface;

0 'is angle between plane containing the back edge of the friction surface and a line drawn from the axis of rotation, to the center of curvature of friction surface; means for advancing a yarn from a source thereof into said opening into contact with said friction surface, an internal guide means positioned within said opening behind said friction surface to guide said yarn under tension over said friction surface and means for guiding said yarn out of the interior of said friction surface on the same side it entered into the interior of said friction surface.

8. The apparatus of claim 7 wherein said friction surface is the interior surface of an insert mounted within the opening of said rotatable member, the axis of symmetry of said insert and said member being coincidental.

9. The apparatus of claim 7 wherein the guide means is rotatably mounted such that the axis of rotation of said guide means and said rotatable member are coincidental.

10. The apparatus of claim 8 wherein the ratio of the diameter of the interior opening of the friction insert to the width of the friction surface of said insert is from about 2 to 40.

11. The apparatus of claim 7 wherein a is less than, or equal to, 1.05. 

1. A process for false twisting yarn by heat setting while it is in a twisted state which comprises advancing a yarn under tension from a source thereof through a temperature zone, contacting said yarn with the interior profiled friction surface of a hollow rotating member, imparting to said yarn both a torsional force and a longitudinal force in the direction of yarn traveled by progressing said yarn diagonally across said profiled friction surface, the path of said yarn in accordance with the formula r1/( r1 - R(Cos theta 2 - Cos theta 1)) a wherein a is less than, or equal to, 1.10 and wherein: r1 is perpendicular distance of front edge of friction surface from axis of rotation; R is radius of curvature of friction surface; theta 1 is angle between plane containing front edge of the friction surface and a line drawn from the axis of rotation, perpendicular thereto, to center of curvature of the friction surface; theta 2 is angle between plane containing the back edge of the friction surface and a line drawn from the axis of rotation, to the center of curvature of friction surface; and simultaneously false twisting said yarn by a substantially static rolling friction generated by a substantially nonslipping contact between said yarns and said rotating friction surface, passing said yarn from said interior profiled friction surface and guiding said yarn under tension out of said interior friction surface on the said side it entered into contact with said friction surface.
 2. The process of claim 1 wherein the threadline initially contacts said friction surface on one side of said rotating member and is guided out of the interior of said rotating member on the same side of said rotating member, not in contact with said friction surface.
 3. The process of claim 1 wherein the tension upstream of the point of initial contact with the interior profiled friction surface of said rotating member is substantially equal to the downstream tension.
 4. The process of claim 1 wherein the yarn approaches the profiled friction surface of the rotating member at an angle of from about 75* to 105* with respect to the axis of rotation of said rotating member.
 5. The process of claim 1 wherein a is less than, or equal to, 1.05.
 6. The process of claim 1 wherein the yarn contacts the friction surface across substantially the whole width of said friction surface.
 7. An apparatus for imparting false twist to textile filaments comprising a radially symmetrical, rotatable member having a substantially circular opening at at least one end thereof, the axis of rotation and axis of symmetry of said rotatable member being coincidental with the axis of symmetry of said circular opening, a friction surface within said opening of said member with said surface having a surface profile defined by the following formula: r1/( r1 - R(Cos theta 2 - Cos theta 1)) a wherein a is less than, or equal to, 1.10 and wherein: r1 is perpendicular distance of front edge of friction surface from axis of rotation; R is radius of curvature of friction surface; theta 1 is angle between plane containing front edge of the friction surface and a line drawn from the axis of rotation, perpendicular thereto, to center of curvature of the friction surface; theta 2 is angle between plane containing the back edge of the friction surface and a line drawn from the axis of rotation, to the center of curvature of friction surface; means for advancing a yarn from a source thereof into said opening into contact with said friction surface, an internal guide means positioned within said opening behind said friction surface to guide said yarn under tension over said friction surface and means for guiding said yarn out of the interior of said friction surface on the same side it entered into the interior of said friction surface.
 8. The apparatus of claim 7 wherein said friction surface is the interior surface of an insert mounted within the opening of said rotatable member, the axis of symmetry of said insert and said member being coincidental.
 9. The apparatus of claim 7 wherein the guide means is rotatably mounted such that the axis of rotation of said guide means and said rotatable member are coincidental.
 10. The apparatus of claim 8 wherein the ratio of the diameter of the interior opening of the friction insert to the width of the friction surface of said insert is from about 2 to
 40. 11. The apparatus of claim 7 wherein a is less than, or equal to, 1.05. 